The present invention is related to a molding device for molding various products in a cavity.
A conventional molding device as shown in FIG. 17 has been proposed. The molding device comprises a fixed mold 113 and a mold-holding member 115. The fixed mold 113 is detachably mounted to a mold-holding member 112 that is fixed to a bed 111. The mold-holding member 115 is mounted so as to reciprocate along guide rails 114 in the front and rear direction (left and right direction as viewed in FIG. 17) with respect to the mold-holding member 112. A movable mold 116 is detachably mounted to the mold-holding member 115. An injection mechanism 117 is arranged at the right side of the bed 111. Liquid metal such as aluminum is fed via the injection mechanism 117 into a cavity that is formed by the fixed mold 113 and the movable mold 116 that are closed to mold a product. The injection mechanism 117 comprises a sleeve 118. The sleeve 118 includes a storing chamber 119 for the molten metal that penetrates through the mold-holding member 112 to be communicated to the fixed mold 113. An injection opening 120 for the molten metal is formed at an outer edge of the sleeve 118. An injection rod 121 is inserted in the storing chamber 119 and is reciprocated by a cylinder 122.
In the above molding device, the molten metal is injected into the storing chamber 119 from the injection opening 120 while the movable mold 116 is in a closed state with respect to the fixed mold 113. Then, the injection rod 121 is moved forward by the cylinder 122 so that the molten metal in the storing chamber 119 is pressed into the cavity. Therefore, the number of process steps of the molding operation is three, including the mold closing, the injection of the molten metal, and the pressing of the molten metal. The efficiency of the molding operation is decreased and manufacturing cost is increased because of the number of process steps.
In the above molding device, the pressure in the cavity is decreased after closing the molds so that the air in the cavity is not mixed with the molten metal during the injection molding. However, if the pressure is decreased to a high negative pressure, outer air penetrates into the storing chamber 119 through a small opening between an outer circumferential surface and an inner circumferential surface of the sleeve 118. The outer air is led into the cavity and fine bubbles are mixed with the molten metal, and the quality of the molding is decreased. Therefore, it is difficult to increase the negative pressure and improve the quality of the molding.